The contagious period for pneumonia lasts several days to a week. The length of time that a person with pneumonia is contagious depends on what causes the infection. If antibiotics are given for the pneumonia, the person is no longer contagious after one day of treatment, according to WebMD.
Pneumonia is caused by bacteria, viruses, parasites or fungi entering the lungs, according to Everyday Health. People do not spread pneumonia; they spread the organisms that cause pneumonia. Pneumococcal pneumonia, the most common bacterial pneumonia, is more prevalent in adults. Viral pneumonias affect children most often, and Legionnaires' disease, an environmental pneumonia, is only contagious to people who have been exposed to contaminated air conditioning systems.